The research proposed in this application has as its primary goal the computer implementation of a statistical simulation model for the study of the development and spread of the AIDS epidemic. The model will presume a heterogeneous population with emphasis on the intravenous drug users who form an important subgroup for harboring and transmitting the AIDS infection. With such a model, it will be possible to predict the course of the epidemic, measure the variability of the prediction, and assess the sensitivity of the outcome to parameters in the model, particularly those that can be modified through intervention programs. This last capability is especially important to policy makers, as it enables them to evaluate the potential effects of various strategies for combatting the epidemic.